Keyboard won't type correctly

sounds like your control key is stuck

That does sound exactly like a stuck modifier key, presumably control as suggested.

Since a reboot didn't fix it and it's not obviously physically stuck, there are two possibilities I can think of:

1) Some kind of catastrophic software failure. Easy to rule out: Boot from the disc that came with the computer and see if they keyboard behaves normally there. If so, it's software, although I have no idea what to try if this were the case. If not, must be hardware.

2) Your keyboard decided to break in a weird way. If it's an external, at least it's easy to replace.

To confirm that it's actually broken (more important if it's a laptop), you could try pulling the key cap off (just pull the key up evenly by its edges using your fingernails or something like a paper clip to pry it with--it should pop off). If the silicone thing underneath is torn or gummed up or something, try fixing it or at least pulling it out so it stops holding the key down. If it's clean and normal looking, maybe it just broke.

Rare, but I've seen similar things happen.

or a lot more likely

3) someone spilled something containing sugar in your keyboard, just enough to make your control key stick, or cover the connector, making it appear to the os as if pressed down all the time.

the easiest way to troubleshoot this is just to try a different keyboard. - presuming that you can remove the one that isn't working right now.. ( basically if you have a desktop )